1. Field of the Invention
The invention relates to a method and apparatus for increasing the collisional energy between particles in a self-colliding beam.
2. Description of the Prior Art
The collisional energy, also known as "center-of-mass" energy, of two bodies of equal mass, colliding head-on, is 4 times greater than the collisional energy obtained in the collision of a single living body with a body of equal mass at rest. This follows from the fact that relative velocity of two particles colliding head-on is 2 v, so the energy of two collision is (1/2) m (2 v).sup.2 =2 mv.sup.2, as opposed to (1/2)mv.sup.2 for a moving particle of velocity v colliding with a stationary particle. The exact energy multiplication factor achievable depends on the masses of two colliding particles. It is equal to (1+m.sub.1 /m.sub.2).sup.2, where m.sub.1 is the beam particle and m.sup.2 the target particle. In the uncommon cases where the beam particle is heavier than the target particle, the multiplication factor can be much greater than 4, e.g. for m.sub.1 /m.sub.2 =9, it is 10,000.
The foregoing realization led to the invention of colliding beams by Wideroe (German Patent No. 876279 (1953). The major disadvantage of the Wideroe device was that the beams collided only once (`single traversal`) which produced too small a number of nuclear reactions to be observable, let alone be practical.
In 1958 O'Neill proposed the concept of storage rings for two beams. This advance made the colliding beam concept practical, because it facilitated `multiple traversal` of the same two beams, thus, the collision rate became more significant.
O'Neill and Richter reduced storage rings to practice in 1960 by making an operational storage ring for electron-electron collisions. A number of colliding beams with storage rings were built in the period 1960 to date, using electron-electron, proton-proton, electron-positron and proton-antiproton beams.
The number of collisions per particle stored in a storage ring is proportional to (particle density).sup.2 .times.(confinement time). Two well-known limitations to the number of collisions of ion storage rings are due to two different effects. The first limitation puts an "intrinsic" limit on the confinement time; the second, to the ion density. The limitations are:
(1) Blow-up of beams due to the beam-beam Coulomb scattering at non-relativistic energies.
This effect makes the use of colliding beams possible only for the high energy particles, i.e. the relativistic particles whose velocity approaches the velocity of light. For protons, it means an energy of 10,000 MeV, or higher. At the energies below 10,000 MeV, the multiple Coulomb scattering (MCS) at the intersection point disperses the particles; the cross sectional area of each beam becomes greater than that of the confining beam tube, the beam particles hit the walls of the vacuum chamber and the beam is destroyed. Since the probability that two colliding particles will undergo the MCS is much higher than that for undergoing nuclear reactions, the low energy beams blow up before any significant reaction takes place. For example, for 1 MeV proton-proton beams, the beam life time against MCS is typically one microsecond (10.sup.-6 second). The probability for MCS is inversely proportional to the beam energy-squared; hence, only at very high energies will the beam blowup effect becomes negligible and the beam lifetime can reach many seconds.
(2) Blow-up due to electrostatic repulsion of the like charged particles within the beam itself.
This effects limits the density of the stored beam to the so-called "space charge limit." The latter is typically 10.sup.8 ions/cc at non-relativistic energies. Since the collision rate is proportional to beam density squared, the space charge limit presents a serious limitation to the collisional rate of the colliding beams and hence to its utility.
The concept of self-colliding orbits was invented in 1969, by Macek and Maglich [Particle Accelerators 1, 121 (1970)] and circumvents both of the beam blow-up problems because of the absence of rings and neutralization of the beam.
With regard to the absence of rings, the single volume magnetic mirror confinement device, generally called a `self-collider`, eliminates storage rings. Since most of the multiple scattering takes place in the center of the self-collider, absence of the storage rings means that MCS does not result in a blowup of the beams. The change of direction due to MCS in the center of the device will not eliminate the scattered particle from the device and the magnetic field will repeatedly return it back to the center.
With regard to neutralization, and in the `self-collider`, positive and negative particles are mixed, thus the stored particles are electrically neutralized which, in turn means absence of the repulsion and absence of the space charge limit. Specifically, in this context, the positively charged deuterium ions are mixed with electrons.
Colliding orbits without the storage rings, were first reduced to practice in 1973 by B. Maglich and co-workers [Nuclear Instruments and Methods 120, 309, (1974) and Applied Physics Letters 26, 609 (1975)]. In that embodiment, an accelerated beam of deuterons of 0.1 MeV was made to collide head-on with itself. Only in a single or multiple passage (5-10 passages) was this accomplished, however, and there was no neutralization of the stored, positively charged, deuterium ions by the ambient electrons. In 1976, Maglich and co-workers succeeded in making a multiturn injection into a self-collider with 1.2 MeV beam of molecular deuterons which resulted in a storage of 0.6 MeV atomic deuterium ions. The self colliding orbits were self-collided 10.sup.7 times per second, but electron trapping into the injected beam did not take place and consequently the density of the orbiting ions was limited by the space charge limit, 10.sup.8 ions per cc and the storage time to 2 seconds, both were insufficient to produce sufficient collisional rates and the practical reaction rates between the stored colliding ions [Ferrer, et al, Nuclear Instruments and Methods, 157, 269 (1978)].
Independently, a proton beam of 0.3 MeV imperfectly mixed with electrons was stored in 1965 in the DCX-1 machine at Oak Ridge National Laboratory, but the destructive plasma type instabilities made it impossible to exceed the space charge limit density of 2.times.10.sup.8 protons per cc. [H. Postma et al, Phys. Rev. Lett. 16, 265 (1966), and J. L. Dunlap et al, Phys. Fluids 9, 199, (1966).] It should be pointed out that the orbits in the DCX-1 machine were mostly concentric orbits rather than the "self-colliding orbits", i.e., the DCX orbits did not pass through the center of the device but, most of them circled the center. It was discovered by Maglich and co-workers that plasma instabilities were not present with the self-colliding (central) orbits at the ion densities of up to 3.times.10.sup.8 ions per cc. [Ferrer et al, Nuclear Instruments and Methods, 157, 269 (1978)].
Summing up the prior art, the presence of space charge limits (failure to neutralize the ions) and that of plasma type instabilities (failure to stabilize) has prevented increases of ion densities above about 10.sup.8 ions per cc, and measurable practical nuclear collisional rates could not be achieved.